CLINICAL PHARMACOLOGY
Mechanism Of Action
Aspirin [acetylsalicylic acid (ASA)] inhibits
prostaglandin synthesis resulting in inhibition of platelet aggregation for
their lifespan of about 7-10 days. The acetyl group of aspirin binds with a
serine residue of cyclooxygenase-1 (COX-1), resulting in irreversible
inactivation of the enzyme. Inhibition of COX-1 prevents conversion of
arachidonic acid to thromboxane A2 (TXA2), which is a potent agonist of
platelet aggregation.
Pharmacodynamics
The dose-response relationship for DURLAZA and immediate
release (IR) aspirin towards COX-1 inhibition was characterized by examining
the inhibition of serum TXB2 and urine 11dehydro-TXB2 at 24 h following a
single dose. Doses over the range of 20 mg to 325 mg for DURLAZA and 5 mg to 81
mg for IR aspirin respectively were studied. Half-maximal inhibition of serum
TXB2 and urine 11-dehydro-TXB2 occurred with doses of DURLAZA (ID50) about
2-fold the dose of immediate release (IR) aspirin. Based on this relationship,
the pharmacodynamic effect of DURLAZA 162.5 mg is similar to that attained with
IR aspirin 81 mg. The mean inhibition of serum TXB2 following DURLAZA (82%) is
lower when compared to IR aspirin 81 mg (93%) following the first dose.
However, upon repeat administration, near maximal inhibition of serum TXB2 is
achieved, similar to what is achieved following repeated daily doses of IR
aspirin.
Pharmacokinetics
Following oral administration, DURLAZA exhibits extended
release of aspirin from the encapsulated microparticles, thereby prolonging the
absorption of aspirin across the GI tract compared to IR aspirin (Figure 1).
Once absorbed, aspirin is metabolized, distributed, and excreted in a manner
similar to that of aspirin absorbed from IR dosage forms.
Figure 1: Mean acetylsalicylic acid concentration-time
profile following single dose administration of 162.5 mg DURLAZA or 81 mg
immediate release ASA
Absorption
Following administration of
DURLAZA, the time to reach peak plasma concentration of aspirin is slightly
longer compared to following IR aspirin dosage form. Median Tmax for DURLAZA is
about 2 h when compared to 1 h following IR aspirin (see Figure 1). The mean Cmax
for DURLAZA is approximately 35% of that following IR aspirin 81 mg. The area
under the plasma concentration-time curve for aspirin following administration
of DURLAZA is approximately 70% of that following IR aspirin. The rate of
DURLAZA absorption is dependent on food, alcohol, and gastric pH.
Distribution
The volume of distribution of
usual doses of aspirin in normal subjects averages approximately 170 mL/kg of
body weight.
Metabolism
Aspirin is rapidly hydrolyzed
in the plasma to salicylic acid such that plasma levels of aspirin following
DURLAZA administration are essentially undetectable 4-8 hours after dosing. In
contrast to immediate release aspirin, measurable levels of salicyclic acid at
24 hours following a single dose of DURLAZA were observed. Salicylic acid is primarily
conjugated in the liver to form salicyluric acid, a phenolic glucuronide, an
acyl glucuronide, and a number of minor metabolites.
Elimination
The mean plasma half-life of aspirin may range from 20 to
60 min. Following therapeutic doses, approximately 10% is found excreted in the
urine as salicylic acid, 75% as salicylic acid, and 10% phenolic and 5% acyl
glucuronides of salicylic acid.
Animal Toxicology And/Or Pharmacology
A single oral dose of 2500 mg/kg (HED 405 mg/kg) DURLAZA
was well-tolerated in the gastrointestional tract of the rat whereas a single
oral dose of IR aspirin ≥ 740 mg/kg (HED 120 mg/kg) caused lethality and
gastric mucosal damage.
Clinical Studies
Chronic Coronary Artery Disease
This indication is supported by the results of six large,
randomized, multi-center, placebo controlled trials of predominantly male
post-MI subjects and one randomized placebo-controlled study of men with
unstable angina pectoris. Aspirin therapy in MI subjects gave about 20%
reduction in the relative risk of the combined endpoint of death or nonfatal
reinfarction . In the study of male unstable angina patients, aspirin reduced
the event rate from 10% in the placebo patients to 5% in the patients treated with
aspirin.
It is also supported by a randomized, multi-center,
double-blind trial designed to assess the effect of aspirin in reducing the
risk of MI in patients with chronic stable angina pectoris. Aspirin reduced the
relative risk of the primary combined endpoint of nonfatal MI, fatal MI, and
sudden death by 34%. The secondary endpoint for vascular events (the first
occurrence of MI, stroke, or vascular death) was also significantly reduced.
Ischemic Stroke And Transient Ischemic Attack (TIA)
In clinical trials of subjects with ischemic stroke or
TIAs, aspirin has been shown to reduce the relative risk of the combined
endpoint of stroke or death and the combined endpoint of TIA, stroke, or death
by about 13 - 18%.